Before cleaning stained glass, you need to check for a couple of issues:

1. Possible chemical reactions from the lead frames that hold each piece in place.
2. Any potential loose pieces. These can cause you to get liquid into the crevices, potentially requiring you to chase drips on either side.

You also need to be aware of a couple of big no-no's:

1. Don't use Dawn when cleaning leaded glass. Dawn can discolor the lead frame.
2. Don't use a water fed pole on stained glass. We know of one window cleaner who did and accidentally pushed out a pane.

The safest method for cleaning stained glass window is using a foam spray cleaner like Sprayaway and a microfiber towel. (Microfiber is key with Sprayaway!)